Fluidic apparatus for air-conditioning systems

ABSTRACT

The present invention provides a fluidic oscillator in an airconditioning system to deliver bursts of air at full volume as the terminal unit oscillates in response to the room thermostat. These bursts of air, short or long, would fulfill the register&#39;&#39;s volume requirements, thus maintaining full room comfort.

United States Patent Oshelroffv 1 Aug. 1, 1972 [54] FLUIDIC APPARATUS FOR AIR- [56] References Cited [72] f t ge g v N UNITED STATES PATENTS nven or: ne em as e as, e

g v 3,275,014 9/1966 Plasko ..137/81.5 Asslgneei Flul d1eh Corporation, Torrance, 3,279,531 10/1966 Bowles ..165/26 Cahf- 3,547,137 12/1970 Chadwick ..l37/81.5 x 22 Filed; 23, 1970 3,596,670 8/1971 Fehr et a1 ..l37/81.5

3,552,413 1 1971 W t 211 Appl.No.: 101,901 al 137/81 5 Related US. Application Data Prim? Hammer-Meyer Assistant Examiner-Ronald C. Capossela [63] Contmuatlon-ln-part of Ser. No. 839,313, July A0mey Anen E. Home),

7, 1969, abandoned.

[57] ABSTRACT [52] US. Cl. ..236/49, 137/815, 165/22,

165/31 23 /1 13 23 /30 The present invention provides a flu1d1c oscillator 1n [51] 1m. (:1. ..F24f1/00 an air-conditioning system to deliver bursts of air at [58] Field of Sear h l37/81,5; 236/12 R, 13 49; full volume as the terminal unit oscillates in response to the room thermostat. These bursts of air, short or long, would fulfill the registersvolume requirements, thus maintaining full room comfort.

27 Claims, 8 Drawing Figures l RETURN A\R 27 AHZCOND FAN OR sung L\| -2"-/L:--26-; T271 3 HEAT uNlT i2? 61 27b 1 c 24 1 1/ a 250. 1' 25b l '1 1 7 22a/ }l 22b/ 'zze/L 12ml ,5 $211: 1 l

i 1 1a lt/ 200. L 20b 20 PATENIEDAU: 1 m2 SHEU 2 0F 2 l I I I E I l \o J 35b 52b 55b /N VENTOR GENE W. OSHEROFF (BILL 752% A 77'0/2NEY FLUIDIC APPARATUS FOR AIR-CONDITIONING SYSTEMS This application is a continuation-in-part of the original application filed July 7, 1969 and having Ser. No. 839,313, now abandoned.

The present invention relates in general to air-conditioning systems and more particularly relates to fluidic apparatus for the improvement of air-conditioning systems.

In air-conditioning systems of the kind used in hotels, motels, office buildings, and the like, air flow to the conditioned space is restricted as the thermostat approaches satisfaction and, as is well known, throttling is the means by which this is done. By throttling is meant that the quantity of air flowing in thesupply duct is varied as thermostatically-controlled dampers open and close. Unfortunately, however, this throttling of the air flow to the conditioned space produces a pressure imbalance in the system which makes suitable temperature control impossible without employing some form of complicated and relatively expensive apparatus to maintain constant volume control at the fans or discharge terminals. Furthermore, the room register has a fixed opening size governed by throw and sound requirements. As the air flow is restricted under thermostatic control, the register velocity falls below its design point, with the result that proper room conditioning cannot be provided because the air is not thrown across the room, Instead, air just runs out of the register and falls to the floor, thereby causing stratification, drafts and discomfort in the conditioned space.

The present invention, through the use of fluidic devices, is intended to and does alleviate these problems. More particularly, the present invention eliminates throttling altogether and this is achieved by means of fluid amplifier devices that act as by-pass valves. Instead of throttling, each by-pass valve, under control of a room thermostat, simply diverts the air to the return system, thereby providing substantially constant room or zone control. Thus, whereas in prior art systems the quantity of air flowing in the supply duct varies as thermostatically-controlled dampers open and close, in any arrangement according to the present invention once the system is balanced it will thereafter deliver a substantially constant air flow at the register on call from the thermostat.

Furthermore, through the use of certain types and arrangements of fluidic devices, a pulse modulation type of air-conditioning system is provided that will accomplish the same results as variable volume, but with better comfort characteristics. More specifically, because of the inherent flow characteristics of fluidic devices, particularly fluidic oscillators, an air-conditioning system according to the present invention delivers independent bursts of air at full volume as the terminal unit oscillates in response to the room thermostat. These bursts of air, short or long, fulfill the registers volume requirements, thereby maintaining the desired room comfort at all times.

It is, therefore, an object of the present invention to provide a pulse modulation type of air-conditioning system.

It is another object of the present invention to provide an air-conditioning system in which independent bursts of air at full volume are passed through the register.

It is a further object of the present invention to provide a pulse modulating control feature for air-conditioning systems.

It is an additional object of the present invention to provide an air-conditioning device programmed by a room thermostat to deliver bursts of air to the conditioned space.

It is still another object of the present invention to provide fluidic oscillator devices for air-conditioning purposes.

It is another and further object of the present invention to provide an air-conditioning system in which throttling is not used to control the air flow therein.

The novel features which are believed to be characteristic of the invention, both as to its organization and method of operation together with further objects and advantages thereof, will be better understood from the following description considered in connection with the accompanying drawings in which several embodiments of the invention are illustrated by way of example. It is to be expressly understood, however, that the drawings are for the purpose of illustration and description only and are not intended as a definition of the limits of the invention.

FIG. 1 is a first and preferred embodiment of a fluidic oscillator for use in an air-conditioning system according to the present invention, and illustrates the thermostat therein in a neutral or center condition in which both of its valves are closed;

FIG. 1(a) is a schematic diagram of the thermostatic apparatus used in the FIG. 1 embodiment showing the thermostatic valves in one extreme condition, namely, one in which one of the valves is closed and the other fully open;

FIG. 1(b) is a schematic diagram of the same thermostatic apparatus showing the thermostatic valves in another extreme condition, namely, one in which the other of the valves is closed and the first valve fully open;

FIG. 2 is a block diagram of an air-conditioning system in which a fluidic oscillator of the type illustrated in FIG. 1 is utilized;

FIG. 3 illustrates another embodiment of a fluidic oscillator according to the present invention;

FIG. 4 illustrates still a third embodiment of a fluidic oscillator of the monostable type;

FIG. 5 illustrates the use of a membrane in a fourth embodiment of the invention; and

FIG. 6 illustrates a modification of the FIG. 1 embodiment.

For a consideration of the invention in detail, reference is now made to the drawings wherein like or similar parts or elements are given like or similar designations throughout the several figures. Referring first to the fluidic valve arrangement illustratively presented in FIG. 1, one valve is of the bistable kind and is shown to include an inlet channel 10 through which the stream of conditioned air flows from the airconditioning systems supply duct, a pair of outlet channels respectively designated 1 la and 1 1b by means of which the air that enters input channel 10 selectively flows either to the room or zone to be air-conditioned or to the systems return duct, a pair of control channels respectively designated 12a and 12b by means of which the above said stream of air can be controlled so as to selectively direct the air to one or the other of the outlet channels, and a chamber 13 located between the inlet and outlet channels and through which the air must pass in going from the inlet channel to the outlet channels. In the embodiment shown, control channels 12a and 12b respectively lead to opposite sides of this chamber 13 in order to exercise the desired control over the air flow, as is well known and understood by those skilled in the art and as will more clearly appear later.

This FIG. 1 embodiment also includes a second bistable-type of fluidic valve device that is coupled between inlet channel and the outlet channels 110 and 11b of the first fluidic valve. This second valve is schematically illustrated in the figure and, like the first device, includes an inlet channel 14, a pair of outlet channels 15a and 15b, and a pair of control channels 160 and 16b. it also includes a chamber between its input and output channels but because the second valve is schematically illustrated, the chamber here cannot be presented. Suffice it to say, therefore, that control channels 16a and 16b are likewise coupled to opposite sides of this chamber in order to exercise the control on the air flowing through this second device necessary to direct the flow to one or the other of its outlet channels 15a and 15b. As shown in the figure, inlet channel 14 is coupled to inlet channel 10 so that a small percentage of the air entering input channel 10 is tapped off and enters input channel 14. As is also shown, outlet channels 15a and 15b respectively connect to control channels 12a and 12b, with the result that air entering one or the other of outlet channels 15a and 15b will flow into and ultimately through its associated control channel to chamber 13.

Finally, the FIG. 1 embodiment includes a pair of Pitot tubes 17a and 17b respectively mounted in outlet channels 1 la and 11b and, as shown by the broken lines in the figure, these Pitot tubes are respectively connected to control channels 160 and 16b. These Pitot tubes are also respectively connected or coupled to a pair of thermostatically-controlled air escape valves 18a and 18b, the thermostat apparatus as a whole being designated 18. The thermostat, which is located in the room or zone to be conditioned, includes the well known bi-metallic coiled strip 180 which moves in a clockwise or counterclockwise direction according to temperature conditions. In addition to the above, the thermostate also includes a pair of leaf or cantilever type spring members 18d and 18e on or to which are respectively mounted a pair of stops or elements 18f and 18g by means of which the valves 18a and 18b are closed and opened. As can be seen from the figure, members 18d and 1&9 are attached or afflxed at one of their ends to strip 18c and are free or unattached at the other of their ends, the stops or elements 18f and 18g being mounted intermediate these ends and in alignment with valves 18a and 18 b.

The thermostatic apparatus schematically illustrated in the figure is well known and widely available in the commercial market place. Accordingly, a more detailed showing of it is not deemed necessary here. Suffice it to say, therefore, that in this kind of thermostatic apparatus, one or the other of escape valves 18a and 18b is closed or open depending upon the position of bi-metallic strip 186, but in no event will both of them be open simultaneously. In this regard, it will be recognized that both valves may, however, be closed simultaneously. Further details concerning the construction and operation of thermostatic apparatus 18 will be provided as needed hereinbelow in connection with the described operation of the FIG. 1 embodiment.

Considering now the operation of this first embodiment, it will be assumed that outlet channel 11a leads to the room or zone to be conditioned, that outlet channel 11b leads to the air-conditioning systems return duct, and that the air flowing through the device, for example cold air, is initially exiting through outlet channel 11b. It will also be initially assumed that in the second fluidic valve device, the conditioned air flowing therethrough is exiting through outlet channel and from this outlet channel to control channel 12a where it enters chamber 13 to impinge against one side of the main stream of conditioned air passing therethrough. Finally, it will be initially assumed that the temperature in the room or the zone to be conditioned is such that in the thermostat located therein, namely, thermostat l8, bi-metallic strip 18c is in its center position, that is to say, in the position shown in FIG. 1, with the result that valves 18a and 18b are both closed.

Accordingly, with these assumptions in mind, a small portion of the air flowing in outlet channel 11b is picked up by Pitot tube 17b wherein it then travels both to control channel 16a and to valve 18b. Since, as previously assumed, valve 18b is closed, this air that is fed back to it cannot escape and it therefore enters control channel wherein the full force thereof is applied to the stream flowing through the chamber of this second fluidic device. As a result and in accordance with well known and established fluidic principles, the direction of this second stream of air is switched from outlet channel 15a to outlet channel 15b. When this happens, this second stream of air is then directed through control channel 12b against the main stream flowing through chamber 13 and this, in turn, causes the main stream to switch its flow from outlet channel 11b to outlet channel 11a. As desired, the conditioned air is now going to the room or zone to be conditioned.

However, it will be recognized that just as soon as the air begins to flow in outlet channel 11a, Pitot tube 17a picks up a small portion of this air and channels it back both to control channel 16b and to valve 180. Since valve 18a is also completely closed, the air thusly sent back likewise cannot escape through valve and, therefore, the air ends up entering control channel 16b wherein the full force thereof is once again applied to the stream flowing through this second fluidic device to switch it from outlet channel 15b back to outlet channel 15a. When this occurs, this second stream of air is once again directed through control channel 12a to chamber 13, thereby causing the main air stream to return to its initially assumed flow pattern, namely, to outlet channel 11b.

The cycle of operation described above repeats itself over and over again so long as thermostat strip 18c is centered and both thermostat valves thereby closed. In short, the two fluidic devices and the thermostat cooperate to produce a pulsed oscillation in which the main air stream switches back and forth equally between outlet channels 11a and 11b and, therefore, equally between the room or zone to be conditioned and the systems return duct. Under the conditions just described, namely, where both thermostatic valves 18a and 18b are closed, the pulses are of equal duration. It should also be mentioned that in accordance with the concept of the invention, the pulses of air to the room or zone to be conditioned are always injected at full volume.

For a further understanding of the operation of the present invention, assume now that bi-metallic strip 180 is in its extreme counterclockwise position, as is illustrated in FIG. 1(a). In this position of strip 180, valve 18b is closed and valve 18a is totally open. As before, it will also be assumed that the conditioned air is initially exiting through outlet channel 11b to the systems return duct. Accordingly, a small portion of the air flowing in outlet channel 1 1b is picked up by Pitot tube 17b by means of which it then flows both to control channel 16a and valve 18b. However, since valve 18b is closed, this air that is fed back enters control channel 16a to cause the second stream of air to switch from outlet channel 150 to outlet channel b. When this happens, this second stream of air is directed through control channel 12b into chamber 13 where it impinges against the main air stream flowing therethrough to cause it to switch from outlet channel 11b to outlet channel 11a and from thence to the room or zone to be conditioned.

With the main stream of air now flowing in outlet channel 11a, Pitot tube 17a picks up a small portion of this air and feeds it back to control channel 16b and valve 18a. However, since valve 18a is now completely open, the air fed back to it by Pitot tube 17a escapes through it, with the result that very little if any of this air enters control channel 16b. Consequently, the main stream of air does not switch'back to outlet channel llb but, rather, continue to flow through outlet channel 11a, and it continues to flow through outlet 11a to the room or zone to be conditioned so long as valve 18a remains in this completely open state. In other words, so long as valve 18a is entirely open, 100 percent of the conditioned air goes to the room or zone to be conditioned and 0 percent goes to the return duct. Of course, valve 18a does not remain completely open for too long a time under these conditions, but what happens when valve 18a is neither fully closed nor open but, rather, somewhere in between, will be taken up later.

Considering now the operation with the bi-metallic strip 180 in its extreme clockwise position, as is illustrated in FIG. 1(b), which means that valve 18b is now the one that is totally open, and assuming again that the conditioned air is initially exiting through outlet channel 11b, a small portion of the air flowing through outlet channel 11b is picked up by Pitot tube 17b and fed back to control channel 16a and valve 18b. In this instance, however, valve 18b is fully open and valve 18a closed, with the result that all the air fed back to valve 18b by Pitot tube 17b escapes through the valve. In consequence thereof, extremely little if any of this air enters control channel 16a, so that the air streaming through the second fluidic device continues to flow through its outlet channel 15a instead of flipping to outlet channel 15b. As will immediately be recognized, therefore, the main stream of air likewise continues to flow through outlet channel 111) to the systems return duct, and this will continue so long as valve 18b remains in this fully open state. Thus, under these conditions, namely, with valve 18a closed and valve 18b fully open, percent of the conditioned air goes to the return duct and 0 percent goes to the room or zone to be conditioned. Here again, of course, valve 18b doesnt remain fully open for very long but, rather, moves towards some condition that is intermediate being fully open or closed.

Thus far, the operation has been described with valves 18a and 18b both closed, with valve 18a fully open and valve 18b closed, and with valve 180 closed and valve 18b fully open, and it was explained that when both valves are closed, the embodiment oscillates with equal pulses of air alternately being directed through outlet channels 11a and 11b, that when valve 18a is fully open the air flows in a DC. (Direct Current) pattern through outlet channel 11a, and that when valve 18b is fully open the air flows in a DC. pattern through outlet channel 11b. It was also explained that the two last mentioned conditions dont remain that way very long and that after awhile an intermediate condition is reached as determined by temperature considerations.

More particularly, when strip 180 is somewhat left of center, that is to say, has moved somewhat in a counterclockwise direction, so that valve 18b is closed and valve 18a is somewhere between being closed and fully open, a constriction exists at valve 18a so that the air fed back to it by Pitot tube 17a cannot escape as easily as it did before when valve 18a was fully open. As a result, some of this air enters control channel 16b and a back pressure begins to build there, and when this pressure reaches the appropriate level it causes the stream of air in outlet channel 15b to flip or switch to outlet channel which, in turn, causes the mainstream of air in outlet channel 1 la to flip or switch to outlet channel 11b, as previously described. The above said appropriate pressure level to bring about these changes is determined by the design considerations of the fluidic devices, as will be recognized by those skilled in the art.

With the main air stream now flowing in outlet channel 11b, some air will be fed back by Pitot tube 17b, as already mentioned. However, with valve 18b closed, the air immediately enters control channel 16a and, as previously described in detail, this quickly leads to the main air stream being switched back to outlet channel 11a. Hence, with valve 18b closed and valve 18a being neither closed nor fully open, once again a pulsed or pulse modulated operation exists but this time, however, the pulses are not of equal duration as they were when both valves where closed. Rather, an oscillation exists in which unequal bursts or pulses of air emanate from outlet channels 11a and 11b, a relatively short pulse out of outlet channel 11b to the return duct and a longer pulse out of outlet channel 11a to the room or zone to be conditioned. Of course, the relative pulse durations will depend on the position of strip which, in turn, will depend on the temperature conditions in the room or zone to be conditioned. For example, in this kind of situation, the air exiting from outlet channels 110 and 11b may be doing so at an 80 to 20 ratio, 80 percent of the air through outlet channel 11a and 20 percent of the air through outlet channel 1 lb, or

in a 60 to 40 ratio, 60 percent of the air through outlet channel 11a and 40 percent of it through outlet channel 11b, etc., the particular ratio of these pulses of air at any time depending on how nearly the thermostatic conditions of the room or zone to be conditioned are satisfied. Needless to say, the further away they are from being satisfied, the longer the pulses through outlet channel 11a, but they become shorter and shorter as the temperature conditions in the room or zone to be conditioned approach the thermostatic setting in that room or zone. At the end, when the temperature conditions in the room or zone are substantially the same as the pre-set thermostatic conditions, the pulses of conditioned air to the room or zone will only be long enough to maintain this substantially satisfied state.

Finally, considering the situation when strip 18c is somewhat to the right of center, that is to say, has moved somewhat in a clockwise direction, so that valve 180 is closed and valve 18b is somewhere between being closed and fully open, a constriction now exists at valve 18b so that the air fed back to it by Pitot tube 17b cannot escape freely as it did when the valve was fully open. Accordingly, for the same reasons as previously presented in connection with valve 18a, namely, a buildup in pressure to the appropriate level, the air flowing through outlet channel 15a flips to outlet channel 15b and, when this occurs, the air flowing through outlet channel llb flips to outlet channel 11a. At this point, Pitot tube 17a feeds back air to control channel 16b and valve 180 which is closed, with the result that the air flow in outlet channel 15b flips back to outlet channel 15a. Correspondingly, the main air flow flips back to outlet channel 11b and the whole above-described cycle starts all over again. Thus, here again, an oscillatory condition exists in which bursts or pulses of air of unequal duration emanate from outlet channels 11a and 11b with the pulses out of outlet channel 11a being of shorter duration than those out of outlet channel 11b. As before, the relative pulse durations will depend on the position of strip 18c at any one time which, it will be remembered, depends on the temperature conditions in the room or zone to be conditioned as compared to the temperature to which thermostat 18 has been set.

It should be mentioned that whether valve 18a or valve 18b is open is determined by whether the thermostat is set to a temperature that is below the temperature of the room or zone to be conditioned or above it. More specifically, valve 18b will be closed and valve 18a open if the thermostat is set below the temperature in the room so that the longer pulses of conditioned air will enter the room or zone. On the other hand, valve 18a will be closed and valve 18b open when the thermostat is set above the temperature in the room. In this latter case, it will be the shorter pulses of conditioned air that go to the room or zone.

Finally, it should also be mentioned that although the operation of the embodiment was described using cold air, the same applies using hot air as the conditioned air.

Reverence is now made to FIG. 2 wherein the utility of a device according to the present invention, such as the FIG. 1 embodiment, is illustrated in an overall airconditioning system in which a number of rooms or zones to be conditioned are designated 20a, 20b, 20c,

etc. The thermostats in the rooms or zones are of the same type as thermostat 18 in FIG. I and they are, therefore, likewise designated 18 in FIG. 2. In each room there are also input and return ports or registers, the input registers in the several rooms respectively being designated 21a, 21b, etc., and the return registers therein respectively being designated 22a, 22b, 22c, etc. In or in close proximity to each room or zone is a fluidic valve arrangement according to the present invention, for example the fluidic valve device shown in FIG. 1, and these are respectively designated 23a, 23b, etc. Finally, as is usually the case the system includes a fan 24, a cooling or heating unit 25, a supply duct 26, and a return duct 27. Supply duct 26 is the main supply duct, but there are also tributary supply ducts leading to the input channels of fluidic devices 23a, 23b, etc., and these tributary supply ducts are respectively designated 26a, 26b, etc. Similarly, there are tributary return ducts and these are respectively designated 27a, 27b, 27c, etc. As is shown in the figure, return duct 27 is coupled to fan 24 and its tributary ducts are respectively coupled both to the return registers and to one of the outlet channels in the fluidic devices, such as outlet channel 11b in FIG. 1. On the other hand, the other of the outlet channels of the various fluidic devices, such as outlet channel 11a in FIG. 1, are respectively coupled to the input registers by means of which the conditioned air is fed to the various rooms or zones. By the same token, the air leaves the rooms or zones by way of the abovesaid output registers.

Assuming that the FIG. 1 embodiment is being used in the FIG. 2 system, each of the fluidic devices 23a, 23b, etc., is exactly as shown in FIG. 1 and functions the same way too. Thus, conditioned air is fed into the input channels of fluidic devices 23a, 23b, etc., and this is respectively done via ducts 26a, 26b, etc. Similarly, this air that flows through these fluidic devices respectively flows either to rooms 20a, 20b, etc., by way of input registers 21a, 21b, etc., or else back to return duct 27 via ducts 27a, 27b, 27c, etc. Of course, this is all done under the respective control of thermostats l8 and in just the same manner as was described in connection with FIG. 1. It should be pointed out, however, and most emphatically so, that each of the fluidic devices acts independently of every other such device, which means not only that they may be operating out of phase with one another but also that their cycle times may be different. It all depends upon the needs of each room or zone to be conditioned, as detected by the thermostat in each room or zone.

For sake of convenience and clarity, it is considered worthwhile to proceed now to FIG. 6 wherein a modified version of the FIG. 1 embodiment is shown. More particularly, the arrangement in FIG. 6 is identical with that of FIG. 1 except in two respects, namely, the direction of Pitot tubes 17a and 17b have been reversed which, in turn, has necessitated a corresponding reversal in the coupling of control channels 16a and 16b with the chamber in the second fluidic valve in the embodiment. Stated differently, whereas Pitot tubes 17a and 17b point upstream in FIG. 1, they point downstream in FIG. 6 and for this reason are designated 17a and 17b instead. Thus, whereas Pitot tubes 17a and 17b scoop up a small amount of air that may be flowing in outlet channels 11a and 11b to produce or apply positive pressures via control channels 16a and 16b, Pitot tubes 17a and 17b, by virtue of the fact that they point downstream, have partial vacuums or negative pressures created in them instead that are then applied through control channels 16a and 16b. What this means is that instead of the air stream being switched from outlet channel a to 15b, or vice versa, by a pushing action, it is switched instead by a pulling action and it is for this reason that it was necessary to reverse the coupling of the control channels, as abovesaid. However, aside from these two variations, the rest of the structure is arranged the same and functions the same as heretofore described and, therefore, its use in the FIG. 2 system should be apparent. Accordingly, no further description of the FIG. 6 species is deemed necessary.

An embodiment of the invention similar to those shown in FIGS. 1 and 6 but somewhat simpler in its construction and operation is shown in FIG. 3 to which reference is now made. As shown, the fluidic device therein, as before, includes an inlet channel 10 by means of which the stream of air enters the device from the air-conditioning systems supply duct (element 26 in FIG. 2), a pair of outlet channels 11a and 11b respectively leading to the room or zone to be conditioned and to the air-conditioning systems return duct (element 27 in FIG. 2), a pair of control channels 12a and 12b, a chamber 13 disposed between the inlet and outlet channels and to which the control channels are coupled so that pressures can be exerted on opposite sides of the air stream flowing therethrough, a pair of Pitot tubes 17a and 17b respectively mounted in outlet channels 11a and 11b and respectively coupled to control channels 12a and 12b, and, finally, thermostatic apparatus 18 of the kind schematically shown in FIG. 1 and previously described in connection therewith. As is illustrated in the figure, this thermostatic apparatus (specifically the valves 18a and 18b therein) is coupled to the junctions of control channels 12a and 12b with Pitot tubes 17a and 17b.

In its operation it will again be assumed initially that the air stream is passing through outlet channel 11a to the room or zone to be conditioned and that the switch to this outlet channel has just occurred. It will also be assumed that thermostatic valve 18a is substantially fully open and thermostatic valve 18b closed. As a result, the air picked up by Pitot tube 17a passes mostly out through open valve 18a and, therefore, insufficient pressure is exerted through control channel 120 to cause the stream to switch back to outlet channel 11b. However, as the room or zone is cooled (or heated) the valve 180 is gradually closed in the manner previously explained. As a result, less of the air from the Pitot tube now escapes through valve 180 and, correspondingly, more of the air enters the control channel. As a further result, the pressure in control channel 12a and against the main air stream flowing through chamber 13 gradually increases until, at the desired temperature level in the room or zone, the pressure is sufficiently great to cause the air stream to flip over to the other side of the chamber and begin its flow through outlet-channel 11b which, it will be remembered, carries the air to the return duct.

As will be readily be recognized, a similar operation occurs while the air is flowing through outlet channel 11b and thermostatic valves 18a and 181; are respectively closed and open. In this instance, as the temperature in the room or zone to be conditioned changes, valve 18b gradually closes and this continues until the air pressure in control channel 12b is sufiiciently great so that when exerted against the air stream in chamber 13, it causes the stream to once again flip or switch over, this time to outlet channel 1 la.

In the third situation, namely, when thermostatic valves 18a and 18b are both closed, the fluidic device will oscillate with equal pulse periods, that is to say, the air stream will flip back and forth between outlet channels 11a and 11b and the duration of the air stream in each channel will be substantially the same.

From this relatively brief description of the FIG. 3 embodiment it will be recognized that although this embodiment is more simply constructed than the FIG. 1 and 6 embodiments heretofore described in detail, it nevertheless provides a pulse-modulation type of airconditioning system in which the conditioned air, always at full force, enters the room or zone as needed. As before, the pulse periods will depend on the state of the thermostatic valves, that is to say, on whether they are closed or open and if one is open, the degree or extent to which it is open. This has all been described and explained before and since the substance of the prior .description and explanation is applicable here in connection with the FIG. 3 embodiment, much of the specific detail has been omitted at this point to avoid being overly redundant.

It will also be recognized from the earlier discussion herein that by reversing both the orientation of the Pitot tubes 17a and 17b and the coupling of control channels 12a and 12b with chamber 13, the device can be modified to operate on the basis of a partial vacuum or negative pressure, as in the case of the FIG. 6 arrangement.

A third embodiment of a fluidic device adapted for air-conditioning purposes is illustrated in FIG. 5 and, as shown therein, includes the usual inlet channel 10, outlet channels lla and 11b, control channels 12a and 12b, Pitot tubes 17a and 17b, and thermostatic apparatus 18 comprising the air escape valves 18a and 18b and the bi-metallic bar 18c. However, this third embodiment also includes a supply chamber, generally designated 30, which tapers down to and connects with inlet channel 10, the air from the supply duct first entering this supply chamber. On opposite sides of this chamber 30 are a pair of openings or ports respectively designated 31a and 31b, and a corresponding pair of hinged doors or closure devices 32a and 32b by means of which the ports can be opened or closed. In the present instance, the hinges for these devices are shown located at 33a and 33b. Further included in this third embodiment are a pair of variable-volume or variablysized chambers generally designated 34 and 35, the variable nature of these chambers being made possible because each includes, as a wall or as part of a wall thereof, a membrane capable of expanding and con tracting according to the above-ambient pressures therein. These membranes are respectively designated 34a and 34b and, as shown in the figure, are coupled to closure devices 32a and 32b by means of mechanical linkages 35a and 35b. As will be seen later, under the influence of membranes 34a and 34b, closure devices 32a and 32b are respectively opened and closed with the aid of these linkages 35a and 35b.

Finally, the FIG. embodiment includes a pair of intermediate chambers, generally designated 36 and 37, that respectively couple, first to opposite sides of chamber 13 and, second, to opposite sides of chamber 30. In the latter instance, the coupling is achieved via ports 31a and 31b and, for this reason, chambers 36 and 37 respectively have a pair of openings 36a and 37a to provide a clear passageway to these ports, as is shown in the figure. Pitot tubes 17a and 17b are respectively intercoupled with variable chambers 34 and 35 as well as with thermostatic valves 18a and 18b, so that air from the Pitot tubes will either enter the chambers or escape through the valves.

Considering now the operation of this embodiment, it will be assumed at the outset that air is flowing in outlet channel 11a and, therefore, that some of this air is being channeled back to the vicinity of chamber 34 via Pitot tube 170. However, assuming that thermostatic valve 18a is closed, or substantially closed, this air that is channeled back therefore enters chamber 34 and causes membrane 34a to expand. With this expansion, closure device 32a is forced to swing open, thereby exposing port 31a to the air entering supply chamber 30. As a result, a portion of the incoming air, as determined by the extent that port 31a is exposed, passes through port 31a and opening 36a into chamber 36 and from there into control channel 12a wherein it is directed against the main air stream flowing through the chamber of this device. As more and more air is fed back into chamber 34, membrane 34a expands more and more and closure device 32a also opens more and more, with the result that more and more air is directed into control channel 12a and against the mainstream. Accordingly, as the pressure builds up, a point is reached when the mainstream switches from outlet channel 11a to outlet channel 11b and back to the return duct. This point is reached when the room or zone is at the desired level of conditioning.

With the switching of the stream, if valve 18b is closed, the air tapped off by Pitot tube 17b enters chamber 35 and the process, as previously described, is repeated. More particularly, membrane 34b expands and thereby forces closure device 32b to swing open which, in turn, exposes port 31b to the air in chamber 30. As previously explained, an ever increasing amount of air enters control channel 12b and, therefore, an ever increasing amount of pressure is brought to bear against the mainstream At substantially the right moment, the main air stream once again switches to outlet channel 11a and flows to the room or zone to be conditioned.

Following this last switch and in the manner previously described, chamber 35 will return to its normal or unexpanded state and chamber 34 will once again enlarge to respectively close and open ports 31b and 31a. A complete cycle of operation when thermostatic valves 18a and 18b are both closed has thus been described. However, enough of an understanding of the operation has been provided to permit anyone skilled in the art to realize that the overall operation of this embodiment is basically the same as those previously described. Accordingly, it is not deemed necessary to again describe the operation with one thermostatic valve open and the other one closed.

A last embodiment of the present invention is illustrated in FIG. 4 and involves a fluidic oscillator of the monostable type. More particularly, in this embodiment, the first fluidic element is of the bistable type, but the second fluidic element is biased so that the air flowing in its inlet channel 14 will normally flow into its outlet channel 15a and from there to control channel 12a. As a result, the main air stream will normally flow through outlet channel 11b. Assuming that outlet channel 11b leads to a return duct, when the conditions are right, the conditions being among those already described, the air entering Pitot tube 17b also enters control channel 16b which has the effect of switching the stream in that fluidic element from outlet channel 15a to outlet channel 15b. When this happens, the air in outlet channel 15b enters and passes through control channel 12b of the larger fluidic element to chamber 13 where it impinges against the mainstream therein to cause it to switch to outlet channel 11a. As has already been mentioned, the air in outlet channel 11a is directed to the room or zone to be conditioned.

Under the control of the thermostat and the valves therein, the air will continue to flow in outlet channel until the room or zone is conditioned to the desired level, at which point the pressure in control channel 16b will drop sufficiently to permit the air stream in outlet channel 15b to return to outlet channel 15a. When this occurs, the main air stream will likewise be returned to outlet channel 11b until the conditions again exist for the process to again be initiated.

In connection with this FIG. 4 embodiment, it will be recognized that it may be modified in the same manner as that in FIG. 1, namely, by reversing the orientation of the Pitot tube and reversing the point of connection of the control channel to employ vacuum or negative pressure rather than positive pressure to switch the air stream from one to the other of the outlet channels.

Although a number of particular arrangements of the invention have been illustrated above by way of example, it is not intended that the invention be limited thereto. Accordingly, the invention should be considered to include any and all modifications, alterations or equivalent arrangements falling within the scope of the annexed claims.

Accordingly, having thus described the invention, what is claimed is:

1. In an air-conditioning system in which conditioned air from a supply duct is selectively directed to a zone to be conditioned and a return duct, apparatus comprising: a primary bistable fluidic amplifier device through which the conditioned air passes, said devices including an inlet channel coupled to the supply duct, first and second outlet channels respectively coupled to the zone to be conditioned and to the return duct, a control chamber located between said inlet and outlet channels, and first and second control channels coupled to said control chamber; means having an element located in at least one of said outlet channels for producing an air pressure in response to conditioned air flowing therein; equipment having at least one valve therein capable of being selectively opened and closed, said one valve being interconnected by means of a feedback channel with said element so that the air pressure therefrom is applied to said one valve; thermostatic means located in the zone to be conditioned and operable in response to temperature variations therein conditioned air between said first and second outlet channels.

2. The apparatus defined in claim 1 wherein said element is a single Pitot tube.

3. The apparatus defined in claim 1 wherein said additional means includes a monostable fluidic amplifier device having an inlet channel coupled to the inlet channel of said bistable amplifier device to tap off some of the conditioned air flowing therein, a pair of outlet channels respectively connecting to said first and second control channels, a control channel connecting to said feedback channel.

4. The apparatus defined in claim 1 wherein said means includes first and second elements respectively mounted in said first and second outlet channels to respectively produce first and second air pressures in response to conditioned air respectively flowing in said first and second outlet channels.

5. The apparatus defined in claim 4 wherein said equipment includes first and second valves respectively interconnected by means of first and second feedback channels to said first and second elements, each of said valves being capable of being selectively opened and closed; wherein said thermostatic means is adapted to selectively open and close said valves in response to temperature variations in the zone to respectively reduce and increase the air pressures in said feedback channels; and wherein said additional means is coupled between said first and second feedback channels and said first and second control channels.

6. The apparatus defined in claim 5 wherein said first and second elements are Pitot tubes.

7. The apparatus defined in claim 5 wherein said additional means are first and second passageways respectively interconnecting said first and second feedback channels with said first and second control channels to respectively apply said first and second air pressures thereto.

8. The apparatus defined in claim 5 wherein said additional means includes another bistable fluidic amplifier device having an inlet channel coupled to the inlet channel of said primary bistable amplifier device to tap off some of the conditioned air flowing therein, a pair of outlet channels respectively connecting to said first and second control channels, and a pair of control channels respectively connecting to said first and second feedback channels.

9. The apparatus defined in claim 5 wherein said additional means includes a supply chamber interposed between the supply duct and said inlet channel and through which the conditioned air passes on its way from the supply duct to the inlet channel, said supply chamber being selectively connected to said first and second control channels, to apply air under pressure thereto, by means of first and second ports, respectively, in the walls of said chamber; and first and second structures respectively coupled between said first and second feedback channels and said first and second parts to respectively open and close said ports in response to the variations of said first and second air pressures.

10. The apparatus defined in claim 9 wherein each of said structures includes a variable-volume chamber having a membrane as one wall thereof, said chamber being coupled to one of said feedback channels to receive the air pressures therefrom, and closure means linked to said membrane and adapted to open and close the associated port in response to the expansion and contraction of said membrane.

11. Pulse modulation air-conditioning apparatus comprising: first and second fluidic amplifier devices with each having an inlet channel, a pair of outlet channels, a control chamber between its inlet channel and its outlet channels, and a pair of control channels connecting to said control chamber, the inlet channel of said second device connecting to the inlet channel of said first device, and the pair of outlet channels of said second device respectively connecting to the pair of control channels of said first device; and means coupled to and between the outlet channels of said first device and the control channels of said second device for selectively applying pressures to said control channels in response to the flow of conditioned air in said outlet channels, said means including thermostaticallycontrolled pressure devices for applying said pressures to said control channels in response to temperature variations in the zone to be conditioned.

12. The pulse modulation air-conditioning apparatus defined in claim 11 wherein said means includes a pair of feedback channels respectively linking the pair of outlet channels of said first amplifier device with the pair of control channels of said second amplifier device, and wherein said thermostatically-controlled pressure devices are also coupled to said feedback channels.

13. The pulse modulation air-conditioning apparatus defined in claim 12 wherein said pressure devices are a pair of valves respectively coupled to said pair of feedback channels, each of said valves capable of being selectively opened and closed, and wherein said means includes a thermostat at the zone to be conditioned for opening and closing said valves in response to the temperature variations in the zone, said valves being adapted so that no more than one valve will be open at any one time and so that both valves may be closed at the same time.

14. The pulse modulation air-conditioning apparatus defined in claim 12 wherein said means further includes a pair of elements respectively mounted in the pair of outlet channels of said first amplifier device and respectively connected to said pair of feedback channels.

15. The pulse modulation air-conditioning apparatus defined in claim 14 wherein said elements are Pitot tubes.

16. An air-conditioning system in which conditioned air from a source of conditioned air is supplied via a supply duct to a plurality of rooms to be conditioned, and in which the air is ultimately returned to said source via a return duct, a pulse-modulation network for supplying bursts of conditioned air to the rooms as needed, said network comprising: a plurality of thermostat devices respectively mounted in said plurality of rooms, a plurality of fluidic amplifier devices respectively coupled to said plurality of rooms, said amplifier devices also being coupled between the supply and return air ducts, each of said amplifier devices being operable in response to signals successively applied thereto to alternately deliver pulses of conditioned air at full force and for variable periods of time to the room associated therewith and to the return air duct, the duration of said pulses varying as the interval between signals; and a plurality of mechanisms respectively coupled between said plurality of thermostat devices and said plurality of amplifier devices, said mechanisms respectively being under the control of said thermostats to produce said signals at intervals corresponding to temperature variations in the rooms.

17. The network defined in claim 16 wherein said signals are air pressures of sufficient magnitude to switch the conditioned air in said fluidic amplifier devices from the rooms to the return air duct and back again, and wherein said mechanisms are air valve devices operable under the control of the respective thermostat devices to regulate the respective magnitudes of said air pressures in accordance with the temperature variations of the rooms.

18. The network defined in claim 17 wherein each mechanism includes a pair of air valves adapted so that one opens as the other closes and vice versa, and wherein each mechanism includes an element that simultaneously opens and closes said pair of valves under the control of the associated thermostat.

19. A system comprising a zone to be air-conditioned; air-conditioning apparatus including a source of conditioned air flowing in a steady stream, a supply duct coupled to said source and through which said stream of conditioned air flows, and a return duct for said conditioned air; fluid-amplifier means coupled between said supply duct, said return duct and said zone, said fluid-amplifier means being operable in response to signals applied thereto to extract pulses of conditioned air of variable duration from said steady stream and deliver them to said zone, the duration of said pulses corresponding to the intervals between said signals; and thermostatic means positioned in said zone and coupled to said fluid-amplifier means for applying said signals thereto at intervals corresponding to the difference between the temperature of the air in said zone and the temperature setting of said thermostatic means.

20. The combination defined in claim 19 wherein said fluid-amplifier means is adapted to deliver all conditioned air to said return duct that is not delivered to said zone.

21. The combination defined in claim 19 wherein said fluid-amplifier means is adapted to pulse modulate said steady stream of conditioned air, said fluid-amplifier means being further adapted to respectively deliver alternate pulses of said modulated conditioned air to said zone and to said return duct.

22. The combination defined in claim 19 wherein said fluid-amplifier means includes first and second outlet channels respectively coupled to said zone and to said return duct, an inlet channel coupled to said supply duct, a control chamber located between said inlet and outlet channels and into which said steady stream of conditioned air flows, and first and second control c anne s cou led to s 'd contr chamb r, said signals being tema ely applied to S3196} control channels to respectively switch the air flowing through said chamber from one outlet channel to the other; and wherein said thermostatic means is coupled between said first and second control channels.

23. The combination defined in claim 22 wherein said fluid-amplifier means further includes first and second elements respectively coupled to said first and second outlet channels to alternately produce first and second air-pressure signals in response to air flowing therein, said first and second elements respectively being coupled to said first and second control channels and to said thermostatic means to feed said signals thereto.

24. The combination defined in claim 23 wherein said thermostatic means includes first and second airescape valves respectively coupled to said first and second elements and opening and closing to apply said signals to said control channels, said thermostatic means being adapted so that both valves are never open at the same time.

25. An air-conditioning system for a zone to be air conditioned, said system comprising: a terminal unit for said zone; means for creating a constant supply of conditioned air; a duct system for circulating the conditioned air, said duct system including a supply duct for delivering said air supply to said terminal unit, a feeder duct coupled between said terminal unit and the zone, and a return duct coupled between said terminal unit and said means, said feeder and return ducts being joined to each other at a switching point in said terminal unit; and switching means at said switching point for switching the supplied conditioned air to the feeder and return ducts alternately and selectively, said switching means being so constructed that it diverts the flow of air into the selected duct at full volume and such that the alternations are of variable duration as determined by the requirements of the zone for conditioned air.

26. A system according to claim 25 wherein the switching means is of the fluidic type, said switching means being employed at the switching point in combination with the feeder and return ducts, and operating free of moving parts other than valves which are moved for setting or positioned to determine the time ratio in alternately delivering air to the feeder and return ducts.

27. A system according to claim 26 including a thermostat in the zone for controlling the functioning of the switching means by changing the positioning or setting of the valves thereof. 

1. In an air-conditioning system in which conditioned air from a supply duct is selectively directed to a zone to be conditioned and a return duct, apparatus comprising: a primary bistable fluidic amplifier device through which the conditioned air passes, said devices including an inlet channel coupled to the supply duct, first and second outlet channels respectively coupled to the zone to be conditioned and to the return duct, a control chamber located between said inlet and outlet channels, and first and second control channels coupled to said control chamber; means having an element located in at least one of said outlet channels for producing an air pressure in response to conditioned air flowing therein; equipment having at least one valve therein capable of being selectively opened and closed, said one valve being inTerconnected by means of a feedback channel with said element so that the air pressure therefrom is applied to said one valve; thermostatic means located in the zone to be conditioned and operable in response to temperature variations therein to open and close said one valve to respectively reduce and increase the air pressure in said feedback channel; and additional means coupled between said feedback channel and said first and second control channels, said additional means applying said pressure variations to said control channels to respectively switch the flow of conditioned air between said first and second outlet channels.
 2. The apparatus defined in claim 1 wherein said element is a single Pitot tube.
 3. The apparatus defined in claim 1 wherein said additional means includes a monostable fluidic amplifier device having an inlet channel coupled to the inlet channel of said bistable amplifier device to tap off some of the conditioned air flowing therein, a pair of outlet channels respectively connecting to said first and second control channels, a control channel connecting to said feedback channel.
 4. The apparatus defined in claim 1 wherein said means includes first and second elements respectively mounted in said first and second outlet channels to respectively produce first and second air pressures in response to conditioned air respectively flowing in said first and second outlet channels.
 5. The apparatus defined in claim 4 wherein said equipment includes first and second valves respectively interconnected by means of first and second feedback channels to said first and second elements, each of said valves being capable of being selectively opened and closed; wherein said thermostatic means is adapted to selectively open and close said valves in response to temperature variations in the zone to respectively reduce and increase the air pressures in said feedback channels; and wherein said additional means is coupled between said first and second feedback channels and said first and second control channels.
 6. The apparatus defined in claim 5 wherein said first and second elements are Pitot tubes.
 7. The apparatus defined in claim 5 wherein said additional means are first and second passageways respectively interconnecting said first and second feedback channels with said first and second control channels to respectively apply said first and second air pressures thereto.
 8. The apparatus defined in claim 5 wherein said additional means includes another bistable fluidic amplifier device having an inlet channel coupled to the inlet channel of said primary bistable amplifier device to tap off some of the conditioned air flowing therein, a pair of outlet channels respectively connecting to said first and second control channels, and a pair of control channels respectively connecting to said first and second feedback channels.
 9. The apparatus defined in claim 5 wherein said additional means includes a supply chamber interposed between the supply duct and said inlet channel and through which the conditioned air passes on its way from the supply duct to the inlet channel, said supply chamber being selectively connected to said first and second control channels, to apply air under pressure thereto, by means of first and second ports, respectively, in the walls of said chamber; and first and second structures respectively coupled between said first and second feedback channels and said first and second parts to respectively open and close said ports in response to the variations of said first and second air pressures.
 10. The apparatus defined in claim 9 wherein each of said structures includes a variable-volume chamber having a membrane as one wall thereof, said chamber being coupled to one of said feedback channels to receive the air pressures therefrom, and closure means linked to said membrane and adapted to open and close the associated port in response to the expansion and contraction of said membrane.
 11. Pulse modulation air-conditioning aPparatus comprising: first and second fluidic amplifier devices with each having an inlet channel, a pair of outlet channels, a control chamber between its inlet channel and its outlet channels, and a pair of control channels connecting to said control chamber, the inlet channel of said second device connecting to the inlet channel of said first device, and the pair of outlet channels of said second device respectively connecting to the pair of control channels of said first device; and means coupled to and between the outlet channels of said first device and the control channels of said second device for selectively applying pressures to said control channels in response to the flow of conditioned air in said outlet channels, said means including thermostatically-controlled pressure devices for applying said pressures to said control channels in response to temperature variations in the zone to be conditioned.
 12. The pulse modulation air-conditioning apparatus defined in claim 11 wherein said means includes a pair of feedback channels respectively linking the pair of outlet channels of said first amplifier device with the pair of control channels of said second amplifier device, and wherein said thermostatically-controlled pressure devices are also coupled to said feedback channels.
 13. The pulse modulation air-conditioning apparatus defined in claim 12 wherein said pressure devices are a pair of valves respectively coupled to said pair of feedback channels, each of said valves capable of being selectively opened and closed, and wherein said means includes a thermostat at the zone to be conditioned for opening and closing said valves in response to the temperature variations in the zone, said valves being adapted so that no more than one valve will be open at any one time and so that both valves may be closed at the same time.
 14. The pulse modulation air-conditioning apparatus defined in claim 12 wherein said means further includes a pair of elements respectively mounted in the pair of outlet channels of said first amplifier device and respectively connected to said pair of feedback channels.
 15. The pulse modulation air-conditioning apparatus defined in claim 14 wherein said elements are Pitot tubes.
 16. An air-conditioning system in which conditioned air from a source of conditioned air is supplied via a supply duct to a plurality of rooms to be conditioned, and in which the air is ultimately returned to said source via a return duct, a pulse-modulation network for supplying bursts of conditioned air to the rooms as needed, said network comprising: a plurality of thermostat devices respectively mounted in said plurality of rooms, a plurality of fluidic amplifier devices respectively coupled to said plurality of rooms, said amplifier devices also being coupled between the supply and return air ducts, each of said amplifier devices being operable in response to signals successively applied thereto to alternately deliver pulses of conditioned air at full force and for variable periods of time to the room associated therewith and to the return air duct, the duration of said pulses varying as the interval between signals; and a plurality of mechanisms respectively coupled between said plurality of thermostat devices and said plurality of amplifier devices, said mechanisms respectively being under the control of said thermostats to produce said signals at intervals corresponding to temperature variations in the rooms.
 17. The network defined in claim 16 wherein said signals are air pressures of sufficient magnitude to switch the conditioned air in said fluidic amplifier devices from the rooms to the return air duct and back again, and wherein said mechanisms are air valve devices operable under the control of the respective thermostat devices to regulate the respective magnitudes of said air pressures in accordance with the temperature variations of the rooms.
 18. The network defined in claim 17 wherein each mechanism includes a pair of air valves adaptEd so that one opens as the other closes and vice versa, and wherein each mechanism includes an element that simultaneously opens and closes said pair of valves under the control of the associated thermostat.
 19. A system comprising a zone to be air-conditioned; air-conditioning apparatus including a source of conditioned air flowing in a steady stream, a supply duct coupled to said source and through which said stream of conditioned air flows, and a return duct for said conditioned air; fluid-amplifier means coupled between said supply duct, said return duct and said zone, said fluid-amplifier means being operable in response to signals applied thereto to extract pulses of conditioned air of variable duration from said steady stream and deliver them to said zone, the duration of said pulses corresponding to the intervals between said signals; and thermostatic means positioned in said zone and coupled to said fluid-amplifier means for applying said signals thereto at intervals corresponding to the difference between the temperature of the air in said zone and the temperature setting of said thermostatic means.
 20. The combination defined in claim 19 wherein said fluid-amplifier means is adapted to deliver all conditioned air to said return duct that is not delivered to said zone.
 21. The combination defined in claim 19 wherein said fluid-amplifier means is adapted to pulse modulate said steady stream of conditioned air, said fluid-amplifier means being further adapted to respectively deliver alternate pulses of said modulated conditioned air to said zone and to said return duct.
 22. The combination defined in claim 19 wherein said fluid-amplifier means includes first and second outlet channels respectively coupled to said zone and to said return duct, an inlet channel coupled to said supply duct, a control chamber located between said inlet and outlet channels and into which said steady stream of conditioned air flows, and first and second control channels coupled to said control chamber, said signals being alternately applied to said control channels to respectively switch the air flowing through said chamber from one outlet channel to the other; and wherein said thermostatic means is coupled between said first and second control channels.
 23. The combination defined in claim 22 wherein said fluid-amplifier means further includes first and second elements respectively coupled to said first and second outlet channels to alternately produce first and second air-pressure signals in response to air flowing therein, said first and second elements respectively being coupled to said first and second control channels and to said thermostatic means to feed said signals thereto.
 24. The combination defined in claim 23 wherein said thermostatic means includes first and second air-escape valves respectively coupled to said first and second elements and opening and closing to apply said signals to said control channels, said thermostatic means being adapted so that both valves are never open at the same time.
 25. An air-conditioning system for a zone to be air conditioned, said system comprising: a terminal unit for said zone; means for creating a constant supply of conditioned air; a duct system for circulating the conditioned air, said duct system including a supply duct for delivering said air supply to said terminal unit, a feeder duct coupled between said terminal unit and the zone, and a return duct coupled between said terminal unit and said means, said feeder and return ducts being joined to each other at a switching point in said terminal unit; and switching means at said switching point for switching the supplied conditioned air to the feeder and return ducts alternately and selectively, said switching means being so constructed that it diverts the flow of air into the selected duct at full volume and such that the alternations are of variable duration as determined by the requirements of the zone for conditioned air.
 26. A system according to claim 25 wherein the swItching means is of the fluidic type, said switching means being employed at the switching point in combination with the feeder and return ducts, and operating free of moving parts other than valves which are moved for setting or positioned to determine the time ratio in alternately delivering air to the feeder and return ducts.
 27. A system according to claim 26 including a thermostat in the zone for controlling the functioning of the switching means by changing the positioning or setting of the valves thereof. 